A variety of cam locking or “self-tightening” fasteners have been disclosed in the prior art. Such fasteners accommodate a workpiece exposed to vibration. Some prior art devices may be found in U.S. Pat. No. 3,263,727 which issued Aug. 2, 1966 to Arthur B. Herpolsheimer; U.S. Pat. No. 3,417,802 which issued Dec. 24, 1968 to Carl O. Oldenkott; and Canadian Pat. No. 1,320364 which issued Jul. 20, 1993 and to the present inventor and is marketed commercially under the trademark DISC-LOCK.
Such devices usually have one or more washer-shaped pieces having inclined cams on one side and a series of ridges on the other. The washers are mounted so that the cam surfaces will mate. In a typical situation, the washers are mounted on a stud between a nut and the work piece.
Vibration or shock will cause the stud or bolt to elongate. The nut tends to rotate loose. A cam locking device prevents this since the cam rise angle is greater than the lead angle of the thread on the bolt. As the nut rotates relative to the washer, the preload is actually increased, further locking the nut.
One shortcoming of the prior art and commercially available self tightening fasteners is that the stacked nut and washer have a combined height which presents a relatively large profile preventing these fasteners from being used in certain situations, e.g. where there is a small fastener clearance dimension.
In my prior disclosure, the self-tightening fastener's washer is captured by an integral skirt that extends from the bottom of the nut. To date, this skirt has always had a thin wall construction to facilitate a swaging operation which flares over the lower end to retain the washer. This thin wall construction, however, is not conducive to threading. Therefore, to provide an adequate number of threads within the fastener, my prior disclosure had a fastener height to washer diameter ratio of at least 0.54 and more typically about 0.65 (e.g., a height to washer diameter ratio of approximately 0.70 for a W′ fastener). While my prior fastener was adequate for some applications, the relatively high profile prevented its use in other applications.
There was therefore a need for a cam locking fastener having both a captive washer and a low profile.
Screws and bolts are threaded fasteners used to fasten two or more objects together. Bolts can be used to fasten two pieces wherein holes in the pieces align and there is access to both sides of the aligned holes—the head of the bolt and the threaded end of the bolt when threaded through the holes are each exposed. A nut can be fastened to the exposed threaded end of the bolt, and the bolt when tightened elastically axially deforms the bolt, creating a tension in the bolt which prevents the nut from backing off. A washer can be used on one or both ends of the aligned holes to disperse force of the bolt and nut over a wider area of the fastened objects. Such an alignment of holes providing for use of a nut and bolt is called a through-hole.
Screws can be used wherein a through-hole is not present. For example, a screw can be used wherein one of the objects includes a through-hole, and a second of the objects includes a drilled hole that ceases in solid material or a blind hole. The object with the through-hole is aligned to the blind hole or a drill is used to create the through-hole and the blind hole. The object with the blind hole can be machined to include threads within the blind hole matching the threads of a screw to be used. In another embodiment, a self-tapping screw can be used in a blind hole constructed of material that is soft enough for the screw to create its own threads. Screws do not include a nut, and instead of having the hardened metal of the nut to fasten and create the tension in the nut to prevent the nut from backing out, screws must depend upon the strength of the material in the blind hole and frictional resistance between the threads of the screw and the blind hole material to prevent the screw from backing out.
Screws can be more likely to back-out than an equivalent nut and bolt design. Such a tendency can be heightened in applications wherein the fastened objects vibrate. Vibration of the objects tends to loosen a screw in a blind hole. Screws utilized in industrial or heavy machinery applications can be exposed to heavy vibration, and loose screws can cause malfunctions or failure in the machinery. One remedy to loosening screws is to frequently check the screws and retighten the screws as needed. Such a method can be labor intensive and potentially hazardous, depending upon a location of the screws to be checked. Another remedy to loosening screws is to utilize an adhesive upon the threads of the screws as the screws are being installed. Such a remedy increases the adhesion of the screw to the material of the blind hole. However, one having skill in the art will appreciate that such a remedy is likely to increase the time that the screw takes to back-out rather than permanently stop the screw from backing out.